The goal of the proposed research is to extend our understanding of the renal tubular excretory transport of organic compounds with particular reference to the role of renal tubular synthesis of uric acid (urate) in the chicken, rat, dog and man. The relations between renal urate synthesis and plasma concentrations of hypoxanthine and xanthine will be studied. The effects of drugs on peritubular and luminal excretory transport of uric acid as well as reabsorption of uric acid will be determined by experimentally differentiating between: 1. the renal excretory transport of urate formed during the transfer of non-renal urate. We will attempt to localize the site of action of drugs such a thiazides, ethacrynic acid, furosemide, pyrazinoic acid and levodopa which have been reported to alter the excretion of urate in man.